The invention relates to use of ultrasonic radiation at relatively low levels into living tissue, for the surgically non-invasive healing treatment of bone fractures.
Duarte U.S. Pat. No. 4,530,360 describes a technique of treating bone defects, such as bone fractures, pseud-arthroses and the like, using a pulsed radio-frequency ultrasonic signal applied via a transducer to the skin of the patient and directing sound waves to the bone defect to be healed. Duarte's teaching is said to proceed from the fact that bone is piezoelectric in nature; instead of inducing a current which promotes bone growth with an external electromagnetic field, or generating such a current directly, the mechanical energy of Duarte's ultrasound is converted to an electric current in the bone, to then and thereby promote healing.
Talish et al. U.S. Pat. Nos. 5,003,965 and 5,186,162 advance the Duarte technique by providing features which favor safety in the patient's periodic use of pulsed ultrahigh frequency acoustic delivery to an afflicted region of the patient's body, by electrically separating a power-supply and pulse generating module from a local low-power radio-frequency generator. The local radio-frequency generator, complete with battery, is contained in a miniaturized enclosure, which also mounts piezoelectric transducer means for patient-operated application to a special mounting fitment that is stabilized by the fixation cast for the patient's damaged limb; and pulse-modulation of local high-frequency output to the transducer is via an optical-fiber link between the power supply/pulse-generating module and the miniaturized enclosure (and its transducer).
The osteogenic properties of Duarte's pulsed ultrahigh-frequency acoustic therapy have been confirmed by others, but it can be said that for the most part these others are non-specific in recommendations for how and where to apply such acoustic therapy with respect to the known fracture location. At least, two German practitioners* are specific in their recommendation that the directional axis of the acoustic signal should be normal to the bone, and at an offsetting longitudinal distance of approximately two inches from the fracture, it being noted that the Knoch/Klug energy level may cause tissue damage if directed at the situs of the fracture. FNT *H.-G. Knoch and W. Klug, "Stimulation of Fracture Healing with Ultrasound, Springer-Verlag, Berlin, Heidelberg 1990 (translation).
The present invention proceeds from an awareness that a relatively low-frequency (e.g. 5 Hz to 10 kHz) and low-intensity (e.g. less than 100 milliwatts/cm.sup.2) acoustic signal has probably the greatest value and effectiveness for osteogenic therapy, but conventional wisdom must concede that such a signal, non-invasively delivered to the body, stands little chance of being therapeutically delivered to a fractured situs. And even if the fractured bone is the tibia, fractured at the skin, and therefore as close as possible for non-invasive access, there is no assurance that the region of confronting separation of bone fragments will receive the low-frequency excitation which is believed to be necessary for initial generation of collagen and callus formation, to close the space or spaces between bone fragments which confront each other across a separating space or gap.